Protecting Quantum Information by Removing Quantum Information

One of the weird aspects of quantum mechanics is that observing a system can change it, causing information to be lost. This is a challenge for quantum computers, which require information is stored in qubits for extended periods of time. Researchers at NIST and other institutions however have found actually protect the information in qubits by causing them to give up information.

Typically, once information is encoded into the quantum states of particles, forming a qubit, one would want to protect it from the environment and any interference that could cause that information to be lost. What the NIST researchers have done though is taken advantage of that interference to protect the information they want. The researchers used two ultraviolet lasers to entangle two beryllium atoms, forming a qubit, and had two partner magnesium ions nearby. With an ultraviolet laser and microwaves, the researchers caused the qubit to release information to the magnesium ions, but that information only concerned properties of the particles besides their entanglement. The magnesium ions were then cooled with multiple lasers, causing that information to be lost to the environment.

Eventually what happens is the qubit enters a ground state where only the desired entanglement is left, and it is protected from electromagnetic fields. Essentially, everything unwanted about the qubit was removed, so only what the researchers wanted was left, making it hard to destroy. The researchers found they could successfully entangle the correct state within milliseconds, 75% of the time, and with more time the accuracy grew to 89%.